It is known to apply electrical stimulation with the object of producing a physiological effect, typically neuromuscular stimulation to activate or exercise a muscle, or stimulation of nerves for pain relief.
Electrical stimulation as practised hitherto is quite a blunt force. It sends electrical stimulation pulses of uniform shape, intensity and duration from one electrode to another. Some known apparatus may allow the user to vary one or more parameters such as frequency, pulse width or amplitude, but the changes are rather crude and do no allow fine control of the waveform within the body. Also, conventional stimulation techniques do not allow for precise targeting of the stimulation onto particular nerves.
It has been proposed (see for example U.S. Pat. No. 5,895,416 and U.S. Pat. No. 5,501,703) to make use of more than two electrodes in such a way as to allow the shape of the electric field to be selected from a number of options. Although these prior proposals appear to give a degree of spatial selectivity they do not permit very accurate targeting of nerves taking account of different types of nerves.